1. Field of the Invention
The present invention relates to a noise suppressor which suppresses noise transmitted through a first current-carrying wire and a second current-carrying wire.
2. Description of the Related Art
Power electronics devices such as switching power supplies, inverters, lighting circuits for lighting fixtures include a power converter circuit which converts power. The power converter circuit includes a switching circuit which converts a direct current into an alternating current with a rectangular wave. Therefore, the power converter circuit produces a ripple voltage with a frequency equivalent to the switching frequency of the switching circuit or noise associated with the switching operation of the switching circuit. The ripple voltage or noise adversely affects other devices. Therefore, it is necessary to arrange a means for reducing the ripple voltage or noise between the power converter circuit and the other devices or lines.
Moreover, recently as a communications technology used for the establishment of a home communication network, power line communications holds promise, and the development of the power line communications has been advanced. In the power line communications, a high frequency signal is superimposed on a power line to establish communication. In the power line communications, noise is produced on the power line by the operations of various electrical and electronic devices connected to the power line, and the noise causes a decline in communication quality such as an increase in error rate. Therefore, a means for reducing noise on the power line is necessary. Moreover, in the power line communications, it is necessary to prevent a communication signal on an indoor power line from being leaked to an outdoor power line.
Noise transmitted through two current-carrying wires includes normal mode (differential mode) noise which causes a potential difference between two current-carrying wires and common mode noise transmitted through two current-carrying wires at the same phase.
Arranging a line filter on a power supply line, a signal line or the like is effective in preventing the noise. As the line filter, a filter including an inductance device (inductor) and a capacitor, that is, a so-called LC filter is commonly used.
FIG. 20 shows an example of a LC filter for normal mode noise prevention in a related art. The LC filter includes a first inductor L101 disposed on a first current-carrying wire 103 and a first capacitor C101 having one end connected to the first current-carrying wire 103 and the other end connected to a second current-carrying wire 104.
FIG. 21 shows an example of a LC filter for common mode noise prevention in a related art. The LC filter includes a first inductor L101 disposed on a first current-carrying wire 103 and a first capacitor C101 having one end connected to the first current-carrying wire 103 and the other end connected to ground. The LC filter further includes a second inductor L102 disposed on a second current-carrying wire 104 and a second capacitor C102 having one end connected to the second current-carrying wire 104 and the other end connected to ground. The first inductor L101 includes a first winding wire 111, and the second inductor L102 includes a second winding wire 112. The first and the second winding wires 111 and 112 are magnetically coupled to each other through winding the first and the second winding wires 111 and 112 around a common core 100 so as to prevent common mode noise in cooperation, thereby the first and the second winding wires 111 and 112 form a common mode choke coil.
The basic structure of such a LC filter is shown in “Transistor Gijutsu SPECIAL No. 44”, CQ Publishing Co., Ltd., issued on Mar. 1, 1994, p 5 (FIG. 6).